Full is as it says. The whole shooting match able to be installed on a PC with no previous windows OS. Can be moved to any PC you own as long as it's only on one machine at a time.

Upgrade version requires a proscribed earlier version of windows to install - probably 98, ME, 2000 or NT

OEM is a version that in theory can only be purchased with a piece of hardware such as a new pc or a new hard drive. Often only has a recovery CD, especially when purchased with a new PC. Again, in theory, it should only be used with that specific hardware as that is what the OEM licences specifies.

Full version keeps your long term options more open. But it is a bit on the dear side!

OK I'm nearly there, just a little clarification.The upgrade looks like my prefered route but is that transferable to a new hard disc in the future?

How do microsoft know that you have a licenced copy of Win98se already running... will I need the 25 digit code? (hey I have that!) will I need the original win98se cd-rom? (hey I have a backup copy of that, but not the original)

And If I was You, steer clear of XP unless you have a specific need to upgrade. I have a Win98se Desktop a WinXP Desktop home and a WinXP home laptop. 98 for me every time its only benefit for what I think is that you can use USB2 if you have the hardware

When you use the upgrade version it will ask you to put your Win98 cd in to check you have a genuine disk.

I have an oem version of WinXP Home and when recently upgrading my system I inadvertenly installed the copy that I had used on my old setup[I changed the Motherboard/cpu/graphics card and hard drive]yet it activated without any problems.Only realised when I found the new package still sealed.

I had bought another copy to go with my upgrade which is now installed on a pc made up with various bits I had lying about the place.